Both high and low birthweight increase the severity of psychotic symptoms, particularly disorganized and negative symptoms, research indicates.
The findings were most notable for low birthweight, say the researchers, and suggest that symptoms of reality distortion, the severity of which were not associated with birthweight, may represent a more distal phenotypic marker in comparison with disorganized and negative symptoms.
"Our results would appear to support the view that disorganized and negative symptoms and underlying cognitive impairments have a neurodevelopmental background," Asko Wegelius (National Institute for Health and Welfare, Helsinki, Finland) and team comment in Psychiatry Research.
A total of 282 patients with a primary psychotic disorder, 178 of whom had schizophrenia, were assessed using the Scales for the Assessment of Positive and Negative Symptoms (SAPS and SANS).
The average birthweight of the group was 3450 g, and 5% of the psychotic disorder patients and 10% of those with schizophrenia had a low birthweight (<2500 g), while a respective 14% and 18% had a high birthweight (>4000 g).
In patients with a primary psychotic disorder, both low and high birthweight were significantly associated with a greater severity of the disorganized symptom bizarre behavior and the negative symptoms affective flattening and attentional impairment.
There was also a linear relationship between birthweight and the disorganized symptom formal thought disorder, with increasing symptom severity associated with lower birthweight.
The same associations were found in patients with schizophrenia, but the relationships between low and high birthweight and the negative symptoms affective flattening and attentional impairment did not reach statistical significance, and the association between low birthweight and attentional impairment was only of borderline significance.
Low birthweight was found to correlate with greater symptom severity than high birth weight in all the statistically significant associations. This, say the researchers, "suggests that prenatal factors associated with LBW [low birthweight] were of particular significance regarding symptom severity."
They add: "The association observed between LBW, and to some extent also HBW [high birthweight], and disorganized symptoms is in line with previous studies depicting an association between low birth weight and poor social adjustment and cognitive impairment in schizophrenia spectrum disorders."
The team says that birthweight may therefore represent a "proxy measure reflecting the influence of various factors, some of which are associated with fetal health."
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